Question

read the excerpt from the riddle of the rosetta stone, by james cross giblin.
another, more complete copy of the same decree that appeared on the stone was found on a slab at philae in 1848. fuller translations of the hieroglyphic text soon followed. a latin version came out in 1851, a french one in 1867, and an english one in 1871. but many of the hieroglyphs on this slab were missing also, so only a few words and phrases could be added to what was already known from the rosetta stone.
which detail from the excerpt develops the idea that scholars faced many challenges in deciphering the meaning of the decree on the rosetta stone?
more complete copy of the same decree
found on a slab at philae in 1848
a latin version came out in 1851
many of the hieroglyphs on this slab were missing

Explanation:

The key is to find a detail that shows a hindrance. "Many of the hieroglyphs on this slab were missing" indicates a problem (missing hieroglyphs) that would make deciphering difficult. The other options just state facts (finding a copy, translations coming out) without showing a challenge.

Answer:

many of the hieroglyphs on this slab were missing